Air Conditioning and other HVAC units for homes and buildings typically have a service valve in the system for charging the system and for recovery of refrigerant. Additionally, the service valve can act as a shut-off to the system and for allowing the flow of refrigerant through the system. The service valve also provides access to hook up manifold gages for servicing the system.
A typical service valve is described for example in U.S. Pat. No. 6,546,952 ('952 patent) incorporated herein by reference. The '952 patent teaches, an air conditioner service valve, comprising: a valve body, the body defining a valve cavity for receiving a valve stem. The valve stem is threadably engaged to the inside of the valve body so that when the valve stem is rotated about its longitudinal access, the valve stem moves inwardly or outwardly depending on the direction of rotation. An O-ring is typically provided around a top portion of the valve stem and tight contact with the inner wall of the cylindrical cavity to enact a seal between the top portion of the valve stem and the inner wall of the valve body to prevent refrigerant leaks, A service valve cap engages the outside of the valve body and encapsulates the cylindrical cavity and the valve stem in order to prevent dirt and moisture from entering the interior of the service valve.
Refrigerant may exert high pressures on the valve stem and valve body, possibly forcing the valve stem out of the valve body, resulting in loss of refrigerant and even the valve stem. This situation can happen most often if the valve stem is rotated outwardly so far as to disengage with the threads of the valve body. Therefore, typical service valves are provided with means of preventing the valve stem from being forced out of the valve body. The '952 patent solves this problem by providing the valve body to include a deformable collar formed on a top portion of the valve body and a first attachment mechanism on an exterior portion of the valve body, the collar selectively deformable between an installation and a retention position, the collar extending a first distance longitudinally from the attachment mechanism when the collar is in the installation position; and a sealing cap for sealing the valve cavity including a base portion and a sealing portion longitudinally extending from the base portion, an inner surface of the sealing portion including a shoulder having an inner portion and a second attachment mechanism for engaging the first attachment mechanism when the collar is in said retention position, wherein the shoulder inner portion abuts a distal end of the deformable collar in the installation position which prevents the second attachment mechanism from engaging the first attachment mechanism.
An older style service valve is similar to that of the '952 patent except it provides a snap ring positioned above the valve stem in an annular grove in the inner wall of the cylindrical cavity as the means for preventing the valve stem from being forced out of the valve body. This type of valve is also described in the '952 patent and illustrated in FIG. 1 of the '952 patent.
Service valves have been known to leak after even just a few years in service, or even when they are practically brand new. Causes of premature leaking may be due to overheating of the valve parts during manufacture or during installation. Alternatively, the O-ring around the stem deteriorates. Regardless of the cause, most of the refrigerant leaking occurs at the O-ring.
Attempts to repair leaky service valves are known in the art. However, most of these methods entail shutting down the air conditioning unit and removing the refrigerant, which can be costly to replace. For example, one way to repair a leaky service valve is to by-pass the valve entirely or to eliminate it from the system. This involves removing the refrigerant, cutting pipes, braising and welding new pipes, and then recharging the system with refrigerant. Likewise, if the old valve is replaced with a new valve, the operation involves removing the refrigerant, cutting out the old service valve, braising and welding, and finally recharging the system. Some service technicians may opt to replace just the O-ring in the valve-stem, which is where most leaks originate. While replacing the O-ring does not require cutting the lines and welding, the refrigerant still has to be removed from the system and then recharged, which is costly. In addition, only older style service valves allow the valve stem to be removed giving access to the O-ring.
Attempts to repair leaky service valves without removing the refrigerant from the system usually involve trying to make the cap leak-proof by coating the valve body threads with thread seal tape, thread lock compounds, and the like. However, the cap is not designed to be leak-proof or to withstand pressure exerted from leaking refrigerant. While these solutions may work temporarily, they rarely provide a long-term solution. In fact service valve caps have been known to deform and crack under the pressure of the leaking refrigerant.
It is an object of the present invention to provide an improved HVAC service valve which prevents refrigerant leaks emanating from the O-ring region of a service valve and a method of repairing leaky service valves of either type described hereinbefore quickly and at a low cost, without cutting pipes, and without losing or having to replace refrigerant in the system because of the repair.